U.S. patent application number 16/867460 was filed with the patent office on 2021-02-25 for wireless power system with object detection.
The applicant listed for this patent is Apple Inc.. Invention is credited to Zaki Moussaoui, Antoin J. Russell, Jukka-pekka J. Sjoeroos.
Application Number | 20210057938 16/867460 |
Document ID | / |
Family ID | 1000004844161 |
Filed Date | 2021-02-25 |
![](/patent/app/20210057938/US20210057938A1-20210225-D00000.png)
![](/patent/app/20210057938/US20210057938A1-20210225-D00001.png)
![](/patent/app/20210057938/US20210057938A1-20210225-D00002.png)
![](/patent/app/20210057938/US20210057938A1-20210225-D00003.png)
![](/patent/app/20210057938/US20210057938A1-20210225-D00004.png)
![](/patent/app/20210057938/US20210057938A1-20210225-D00005.png)
![](/patent/app/20210057938/US20210057938A1-20210225-D00006.png)
![](/patent/app/20210057938/US20210057938A1-20210225-D00007.png)
United States Patent
Application |
20210057938 |
Kind Code |
A1 |
Russell; Antoin J. ; et
al. |
February 25, 2021 |
Wireless Power System With Object Detection
Abstract
A wireless power system has a wireless power transmitting device
and a wireless power receiving device. The wireless power
transmitting device may be a wireless charging mat or other device
with one or more wireless power transmitting coils for transmitting
wireless power signals. The wireless power receiving device may be
a portable electronic device with one or more wireless power
receiving coils for receiving the transmitted wireless power
signals. The wireless power transmitting device may have foreign
object detection coils. Q-factor measurements may be made on the
transmitting coil during wireless power transmission and/or voltage
measurements may be made using the foreign object detection coils
to detect whether a foreign object is present. The foreign object
detection coils may include overlapping coils with different
winding patterns to enhance foreign object detection coverage.
Inventors: |
Russell; Antoin J.; (San
Francisco, CA) ; Sjoeroos; Jukka-pekka J.;
(Cupertino, CA) ; Moussaoui; Zaki; (San Carlos,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Apple Inc. |
Cupertino |
CA |
US |
|
|
Family ID: |
1000004844161 |
Appl. No.: |
16/867460 |
Filed: |
May 5, 2020 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
62889162 |
Aug 20, 2019 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02J 50/12 20160201;
H02J 50/60 20160201; G01V 3/10 20130101; H01F 38/14 20130101 |
International
Class: |
H02J 50/60 20060101
H02J050/60; H02J 50/12 20060101 H02J050/12; H01F 38/14 20060101
H01F038/14; G01V 3/10 20060101 G01V003/10 |
Claims
1. A wireless power transmitting device for transmitting wireless
power to a wireless power receiving device, comprising: wireless
power transmitting circuitry including a wireless power
transmitting coil configured to transmit wireless power signals;
foreign object detection coils of at least first and second
different winding patterns overlapping the wireless power
transmitting coil; and control circuitry configured to monitor for
the presence of a foreign object using the foreign object detection
coils.
2. The wireless power transmitting device of claim 1 wherein the
first winding pattern comprises a spiral winding pattern.
3. The wireless power transmitting device of claim 2 wherein the
second winding pattern comprises a figure eight winding
pattern.
4. The wireless power transmitting device of claim 1 wherein the
foreign object detection coils include a first set of foreign
object detection coils that are of the first winding pattern and a
second set of foreign object detection coils that are of the second
winding pattern.
5. The wireless power transmitting device of claim 4 wherein there
are at least four foreign object detection coils of the first
winding pattern in the first set.
6. The wireless power transmitting device of claim 5 wherein there
are at least four foreign object detection coils of the second
winding pattern in the second set.
7. The wireless power transmitting device of claim 6 wherein the
first winding pattern comprises one or more spiral coil winding
pattern(s) and wherein the second winding pattern comprises one or
more figure eight winding pattern(s).
8. The wireless power transmitting device of claim 7 wherein each
of the foreign object detection coils has a ring-quarter-segment
outline.
9. The wireless power transmitting device of claim 8 wherein each
of the foreign object detection coils in the first set overlaps a
respective one of the foreign object detection coils in the second
set.
10. The wireless power transmitting device of claim 9 wherein the
wireless power transmitting coil has multiple turns and wherein
each of the foreign object detection coils completely overlaps the
turns and does not overlap a central opening in the wireless power
transmitting coil.
11. The wireless power transmitting device of claim 1 wherein each
of the foreign object detection coils of the first winding pattern
overlaps and shares a common shape with a respective one of the
foreign object detection coils of the second winding pattern.
12. A wireless power transmitting device for transmitting wireless
power to a wireless power receiving device, comprising: wireless
power transmitting circuitry; a coil; and control circuitry
configured to gather Q-factor measurements on the coil to detect
foreign objects while the wireless power transmitting circuitry is
driving the coil with a coil drive signal to transmit wireless
power to the wireless power receiving device.
13. The wireless power transmitting device of claim 12 wherein the
wireless power transmitting device comprises a foreign object
detection coil and wherein the wireless power transmitting
circuitry comprises: a wireless power transmitting coil through
which the coil drive signal flows; and an inverter configured to
supply the coil drive signal to the wireless power transmitting
coil, wherein the coil drive signal comprise an alternating-current
signal.
14. The wireless power transmitting device of claim 13 wherein the
control circuitry comprises measurement circuitry configured to
gather the Q-factor measurements by measuring resonance
characteristic(s) in the coil drive signal.
15. The wireless power transmitting device of claim 14 wherein the
wireless power transmitting circuitry comprises a capacitor coupled
across the coil.
16. The wireless power transmitting device of claim 15 wherein the
control circuitry is configured to halt transmission of the
wireless power in response to detecting that one of the Q-factor
measurements is below a predetermined threshold value.
17. A wireless power transmitting device for transmitting wireless
power to a wireless power receiving device, comprising: wireless
power transmitting circuitry including a wireless power
transmitting coil configured to transmit wireless power signals; a
spiral-winding foreign object detection coil with a spiral winding
pattern; and a figure-eight-winding foreign object detection coil
with a figure-eight winding pattern.
18. The wireless power transmitting device of claim 17 wherein the
spiral-winding foreign object detection coil and the
figure-eight-winding foreign object detection coil overlap each
other.
19. The wireless power transmitting device of claim 18 wherein the
spiral-winding foreign object detection coil and the
figure-eight-winding foreign object detection coil at least
partially overlap the wireless power transmitting coil.
20. The wireless power transmitting device of claim 19 further
comprising: a layer of magnetic material; and printed circuit with
metal traces forming the spiral-winding foreign object detection
coil and the figure-eight-winding foreign object detection coil,
wherein the printed circuit is interposed between the wireless
power transmitting coil and the layer of magnetic material.
21. The wireless power transmitting device of claim 19 further
comprising: a layer of magnetic material; and printed circuit with
metal traces forming the spiral-winding foreign object detection
coil and the figure-eight-winding foreign object detection coil,
wherein the printed circuit is interposed between the wireless
power transmitting coil and the layer of magnetic material to
reduce sensitivity to misalignment of the wireless power receiving
device with respect to the wireless power transmitting coil.
Description
[0001] This application claims the benefit of provisional patent
application No. 62/889,162, filed Aug. 20, 2019, which is hereby
incorporated by reference herein in its entirety.
FIELD
[0002] This relates generally to power systems, and, more
particularly, to wireless power systems for charging electronic
devices.
BACKGROUND
[0003] In a wireless charging system, a wireless power transmitting
device such as a charging mat wirelessly transmits power to a
wireless power receiving device such as a portable electronic
device. The portable electronic device has a coil and rectifier
circuitry. The coil of the portable electronic device receives
alternating-current wireless power signals from the wireless
charging mat. The rectifier circuitry converts the received signals
into direct-current power. To ensure satisfactory operation, the
wireless charging system may have circuitry to detect foreign
objects.
SUMMARY
[0004] A wireless power system has a wireless power transmitting
device and a wireless power receiving device. The wireless power
transmitting device may be a wireless charging mat or other device
with one or more wireless power transmitting coils for transmitting
wireless power signals. The wireless power receiving device may be
a portable electronic device with one or more wireless power
receiving coils for receiving the transmitted wireless power
signals.
[0005] The wireless power transmitting device has foreign object
detection coils of one or more winding types. Q-factor measurements
may be made on a transmitting coil during wireless power
transmission and/or magnetic field measurements may be made using
the foreign object detection coils to detect whether a foreign
object is present.
[0006] The foreign object detection coils may include overlapping
coils of different types. For example, the foreign object detection
coils may include a first set of coils with spiral windings and
second set of coils with figure-eight windings. By overlapping the
first coils and second coils, foreign object detection accuracy can
be enhanced.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a schematic diagram of an illustrative wireless
power system that includes a wireless power transmitting device and
a wireless power receiving device in accordance with an
embodiment.
[0008] FIG. 2 is a graph of an illustrative wireless power
transmitter signal in accordance with an embodiment.
[0009] FIG. 3 is a circuit diagram showing illustrative measurement
circuitry in a wireless power transmitter in accordance with an
embodiment.
[0010] FIGS. 4, 5, 6, and 7 are diagrams of illustrative wireless
power transmitter coils and foreign object detection coils in
accordance with an embodiment.
[0011] FIG. 8 is a cross-sectional side view of an illustrative
wireless power system in accordance with an embodiment.
[0012] FIG. 9 is a diagram of an illustrative foreign object
detection coil with a spiral winding in accordance with an
embodiment.
[0013] FIG. 10 is a diagram of an illustrative foreign object
detection coil with a figure eight winding forming a pair of
subcoils with respective clockwise and counterclockwise winding
senses in accordance with an embodiment.
[0014] FIG. 11 is a cross-sectional side view of a portion of an
illustrative wireless power transmitting coil and overlapping
subcoils in a foreign object detection coil in accordance with an
embodiment.
[0015] FIG. 12 is a graph showing potential output readings from
overlapping spiral and figure eight foreign object detection coils
as a function of foreign object location in accordance with an
embodiment.
DETAILED DESCRIPTION
[0016] A wireless power system includes a wireless power
transmitting device such as a wireless charging mat. The wireless
power transmitting device wirelessly transmits power to a wireless
power receiving device such as a wristwatch, cellular telephone,
tablet computer, laptop computer, or other electronic equipment.
The wireless power receiving device uses power from the wireless
power transmitting device for powering the device and for charging
an internal battery.
[0017] Wireless power is transmitted from the wireless power
transmitting device to the wireless power receiving device using
one or more wireless power transmitting coils to charge a battery
in the wireless power receiving device and/or to power other load
circuitry. The wireless power receiving device has one or more
wireless power receiving coils coupled to rectifier circuitry that
converts received wireless power signals into direct-current
power.
[0018] An illustrative wireless power system (wireless charging
system) is shown in FIG. 1. As shown in FIG. 1, wireless power
system 8 includes a wireless power transmitting device such as
wireless power transmitting device 12 and includes a wireless power
receiving device such as wireless power receiving device 24.
Wireless power transmitting device 12 includes control circuitry
16. Wireless power receiving device 24 includes control circuitry
30. Control circuitry in system 8 such as control circuitry 16 and
control circuitry 30 is used in controlling the operation of system
8. This control circuitry may include processing circuitry
associated with microprocessors, power management units, baseband
processors, digital signal processors, microcontrollers, and/or
application-specific integrated circuits with processing circuits.
The processing circuitry implements desired control and
communications features in devices 12 and 24. For example, the
processing circuitry may be used in selecting coils, determining
power transmission levels, processing sensor data and other data to
detect foreign objects and perform other tasks, processing user
input, handling negotiations between devices 12 and 24, sending and
receiving in-band and out-of-band data, making measurements, and
otherwise controlling the operation of system 8. In an illustrative
configuration, the processing circuitry of device 12 uses foreign
object detection coils to monitor for the presence of foreign
objects such as coins, paper clips, credit cards, etc. and takes
appropriate action (e.g., halting power transmission) in response
to detecting that a foreign object is present.
[0019] Control circuitry in system 8 may be configured to perform
operations in system 8 using hardware (e.g., dedicated hardware or
circuitry), firmware and/or software. Software code for performing
operations in system 8 is stored on non-transitory computer
readable storage media (e.g., tangible computer readable storage
media) in control circuitry 8. The software code may sometimes be
referred to as software, data, program instructions, instructions,
or code. The non-transitory computer readable storage media may
include non-volatile memory such as non-volatile random-access
memory (NVRAM), one or more hard drives (e.g., magnetic drives or
solid state drives), one or more removable flash drives or other
removable media, or the like. Software stored on the non-transitory
computer readable storage media may be executed on the processing
circuitry of control circuitry 16 and/or 30. The processing
circuitry may include application-specific integrated circuits with
processing circuitry, one or more microprocessors, a central
processing unit (CPU) or other processing circuitry.
[0020] Power transmitting device 12 may be a stand-alone power
adapter (e.g., a wireless charging mat or charging puck that
includes power adapter circuitry), may be a wireless charging mat
or puck that is coupled to a power adapter or other equipment by a
cable, may be a portable device, may be equipment that has been
incorporated into furniture, a vehicle, or other system, may be a
removable battery case, or may be other wireless power transfer
equipment. Illustrative configurations in which wireless power
transmitting device 12 is a wireless charging mat are sometimes
described herein as an example.
[0021] Power receiving device 24 may be a portable electronic
device such as a wristwatch, a cellular telephone, a laptop
computer, a tablet computer, an accessory such as an earbud, or
other electronic equipment. Power transmitting device 12 may be
coupled to a wall outlet (e.g., an alternating current power
source), may have a battery for supplying power, and/or may have
another source of power. Power transmitting device 12 may have an
alternating-current (AC) to direct-current (DC) power converter
such as AC-DC power converter 14 for converting AC power from a
wall outlet or other power source into DC power. DC power may be
used to power control circuitry 16. During operation, a controller
in control circuitry 16 uses power transmitting circuitry 52 to
transmit wireless power to power receiving circuitry 54 of device
24. Power transmitting circuitry 52 may have switching circuitry
(e.g., inverter circuitry 61 formed from transistors) that is
turned on and off based on control signals provided by control
circuitry 16 to create AC current signals through one or more
wireless power transmitting coils such as wireless power
transmitting coils 36. These coil drive signals cause coil(s) 36 to
transmit wireless power. Coils 36 may be arranged in a planar coil
array (e.g., in configurations in which device 12 is a wireless
charging mat) or may be arranged to form a cluster of coils (e.g.,
in configurations in which device 12 is a wireless charging puck).
In some arrangements, device 12 (e.g., a charging mat, puck, etc.)
may have only a single coil. In other arrangements, a wireless
charging device may have multiple coils (e.g., two or more coils,
5-10 coils, at least 10 coils, 10-30 coils, fewer than 35 coils,
fewer than 25 coils, or other suitable number of coils).
[0022] As the AC currents pass through one or more coils 36,
alternating-current electromagnetic (e.g., magnetic) fields
(wireless power signals 44) are produced that are received by one
or more corresponding receiver coils such as coil(s) 48 in power
receiving device 24. Device 24 may have a single coil 48, at least
two coils 48, at least three coils 48, at least four coils 48, or
other suitable number of coils 48. When the alternating-current
electromagnetic fields are received by coil(s) 48, corresponding
alternating-current currents are induced in coil(s) 48. Rectifier
circuitry such as rectifier circuitry 50, which contains rectifying
components such as synchronous rectification
metal-oxide-semiconductor transistors arranged in a bridge network,
converts received AC signals (received alternating-current signals
associated with electromagnetic signals 44) from one or more coils
48 into DC voltage signals for powering device 24.
[0023] The DC voltage produced by rectifier circuitry 50 (sometime
referred to as rectifier output voltage Vrect) can be used in
charging a battery such as battery 58 and can be used in powering
other components in device 24. For example, device 24 may include
input-output devices 56 such as a display, touch sensor,
communications circuits, audio components, sensors, light-emitting
diode status indicators, other light-emitting and light detecting
components, and other components and these components (which form a
load for device 24) may be powered by the DC voltages produced by
rectifier circuitry 50 (and/or DC voltages produced by battery
58).
[0024] Device 12 and/or device 24 may communicate wirelessly using
in-band or out-of-band communications. Device 12 may, for example,
have wireless transceiver circuitry 40 that wirelessly transmits
out-of-band signals to device 24 using an antenna. Wireless
transceiver circuitry 40 may be used to wirelessly receive
out-of-band signals from device 24 using the antenna. Device 24 may
have wireless transceiver circuitry 46 that transmits out-of-band
signals to device 12. Receiver circuitry in wireless transceiver 46
may use an antenna to receive out-of-band signals from device 12.
In-band transmissions between devices 12 and 24 may be performed
using coils 36 and 48. With one illustrative configuration,
frequency-shift keying (FSK) is used to convey in-band data from
device 12 to device 24 and amplitude-shift keying (ASK) is used to
convey in-band data from device 24 to device 12. Power may be
conveyed wirelessly from device 12 to device 24 during these FSK
and ASK transmissions.
[0025] It is desirable for power transmitting device 12 and power
receiving device 24 to be able to communicate information such as
received power, states of charge, and so forth, to control wireless
power transfer. However, the above-described technology need not
involve the transmission of personally identifiable information in
order to function. Out of an abundance of caution, it is noted that
to the extent that any implementation of this charging technology
involves the use of personally identifiable information,
implementers should follow privacy policies and practices that are
generally recognized as meeting or exceeding industry or
governmental requirements for maintaining the privacy of users. In
particular, personally identifiable information data should be
managed and handled so as to minimize risks of unintentional or
unauthorized access or use, and the nature of authorized use should
be clearly indicated to users.
[0026] Control circuitry 16 has external object measurement
circuitry 41 that may be used to detect external objects on the
charging surface of device 12 (e.g., on the top of a charging mat
or, if desired, to detect objects adjacent to the coupling surface
of a charging puck). Circuitry 41 can detect foreign objects such
as coils, paper clips, and other metallic objects and can detect
the presence of wireless power receiving devices 24 (e.g.,
circuitry 41 can detect the presence of one or more coils 48).
During object detection and characterization operations, external
object measurement circuitry 41 can be used to make measurements on
coils 36 and/or on foreign object detection coils 70 to determine
whether any devices 24 are present on device 12.
[0027] In an illustrative arrangement, measurement circuitry 41 of
control circuitry 16 contains signal generator circuitry (e.g.,
oscillator circuitry for generating AC probe signals at one or more
probe frequencies, a pulse generator that can create impulses so
that impulse responses can be measured to gather inductance
information, Q-factor information, etc.) and signal detection
circuitry (e.g., filters, analog-to-digital converters, impulse
response measurement circuits, etc.). In some configurations,
Q-factor measurements and other measurements may be made during
wireless power transfer operations. Switching circuitry in device
12 may be used to switch desired coils into use during wireless
power transmission and/or foreign object detection operations.
[0028] Measurement circuitry 43 in control circuitry 30 and/or
measurement circuitry 41 in control circuitry 16 may be used in
making current and voltage measurements. Based on this information
or other information, control circuitry 30 can configure rectifier
circuitry 50 to help enhance wireless power reception by coils
48.
[0029] FIG. 2 is a graph showing an illustrative wireless power
transmitting signal during wireless power transmission. Wireless
power transmitting coil signal 72 (e.g., coil voltage) is
characterized by an alternating-current waveform that is
established by inverter 61 as inverter 61 drives a wireless power
transmission coil. In the example of FIG. 2, this waveform is a
square wave. Other types of alternating-current (AC) waveforms may
be supplied, if desired. The frequency of the AC drive signal may
be 10 kHz to 1 MHz, at least 50 kHz, less than 300 kHz, or other
suitable frequency.
[0030] As shown in FIG. 2, ringing 74 may be induced in wireless
power transmitting coil signal 72 (e.g., ringing resulting from
each square wave cycle of the AC drive signal and/or ringing
resulting from impulses applied separately to the wireless power
transmitting coil by control circuitry 16 during wireless power
transmission). Using analog-to-digital converter circuitry, peak
detection circuitry, envelope detection circuitry, and/or other
measurement circuitry 41 in control circuitry 16, the magnitude and
frequency of the ringing component of the wireless power
transmitting coil signal and decay envelope 76 can be measured,
thereby allowing coil parameters such as inductance L and Q factor
to be measured. When no foreign object is present, the decay
envelope may have a shape of the type shown by illustrative decay
envelope 76 (as an example). When a foreign object is present, a
damped response (see, e.g., damped envelope 76') may be
exhibited.
[0031] FIG. 3 is a circuit diagram of an illustrative transmitting
coil circuit. As shown in FIG. 3, measurement circuitry 41 may have
a voltage sensor that is configured to measure signal 72 (including
the ringing portion of signal 72) on wireless power transmitting
coil 36. The components of FIG. 3 (e.g., coil 36 and capacitor C)
form a parallel resonant circuit which is tuned to a measurable
frequency (e.g., a frequency of at least 0.2 MHz, at least 0.5 MHz,
about 1 MHz, less than 2 MHz, less than 1.5 MHz, or other suitable
frequency). Capacitor C may be used to reduce the frequency of
ringing 74. The value of capacitor C may be at least 0.2 nF, at
least 2 nF, 22 nF, less than 200 nF, less than 400 nF, or other
suitable value. In the absence of capacitor C, the frequency of
ringing 74 may be tens of MHz, which can pose measurement
challenges. In the presence of capacitor C, which is coupled across
coil 36, the frequency of ringing 74 may be reduced (e.g., to
hundreds of kHz, 1 MHz, or other suitable frequency), thereby
facilitating measurement of ringing 74 with measurement circuitry
41.
[0032] During operation, control circuitry 16 can use measurement
circuitry 41 to measure coil characteristics such as Q factor
(e.g., by measuring decay envelope 76) to determine whether a
foreign object is present on coil 36. In the presence of foreign
object s (e.g., metallic objects), wireless power signals will
induce eddy currents in the foreign object that will create lowered
values of Q factor. In response to detecting that the measured
value of Q is less than a predetermined threshold (or using other
suitable detection criteria), control circuitry 16 can conclude
that a foreign object is likely present and can take appropriate
action (e.g., by notifying a user of system 8, by halting wireless
power transmission, by reducing the amount of power being
transmitted to a relatively low level, etc.). The analysis of the
ringing signal can take place during power transmission operations,
so power transmission need not be interrupted to detect foreign
objects.
[0033] If desired, control circuitry 16 can detect foreign objects
using foreign object detection coils 70. Coils 70 may be arranged
to fully or partially overlap one or more of coils 36. FIGS. 4, 5,
6, and 7 show how coils 70 may include four overlapping layers of
coils that are configured to provide foreign object detection for
an overlapped transmitting coil 36. In the example of FIGS. 4 and
5, coils 70 form segments of a ring. The layout of coils 70 differs
between FIG. 4 and to enhance detection sensitivity. In the example
of FIGS. 6 and 7, coils 70 have the shape of circular sectors
(e.g., wedges). The patterns of coils 70 in FIGS. 6 and 7 differ
from each other and differ from the coil patterns of coils 70 in
FIGS. 4 and 5 to create sensitivity in different areas and thereby
enhance foreign object detection coverage. There are four layers of
coils 70 and 16 coils 70 in total in the illustrative configuration
of FIGS. 4, 5, 6, and 7. In general, there may be one layer of
coils 70, at least two layers of coils 70, at least three layers of
coils 70, at least four layers of coils 70, or other suitable
number of foreign object detection coil layers. Coils 70 may be
formed from signal lines such as metal traces on flexible printed
circuit substrates and/or other substrates, metal wires, or other
signal paths. In some configurations, coils 70 may include spiral
coils and/or figure eight coils.
[0034] FIG. 8 is a cross-sectional side view of system 8. In the
illustrative configuration of FIG. 8, device 12 has a single
wireless power transmitting coil 36 that overlaps flexible printed
circuit 78. A layer of magnetic material such as ferrite layer 80
may be overlapped by coil 36 and flexible printed circuit 78.
Foreign object detection coils 70 are formed from metal traces in
flexible printed circuit 78. Flexible printed circuit 78 is
interposed between coil 36 and the layer of magnetic material
(e.g., layer 80). Misalignment of wireless power receiving device
24 creates unbalance between detection coil voltages, which can, in
some situations, mimic the appearance of a foreign object. By
placing printed circuit 78 below coil(s) 36, printed circuit 78 and
coils 70 are interposed between wireless power transmitting coil 36
and ferrite layer 80 to reduce sensitivity to misalignment of
wireless power receiving device 24 with respect to wireless power
transmitting coil 36.
[0035] The circuitry of device 12 may be formed from components 82
mounted to printed circuit 84. Connector 86 electrically couples
the circuitry on printed circuit 84 to foreign object detection
coils 70 in printed circuit 78. Wires (e.g., lengths of Litz wire)
electrically couple inverter 61 to respective terminals of coil
36.
[0036] Foreign objects such as foreign object 90 may be located
above coil 36 (e.g., at a distance R from the center of coil 36).
Control circuitry 16 uses foreign object detection coils 70 to
measure magnetic fields B to monitor for the presence of objects
such as object 90.
[0037] To enhance detection sensitivity, foreign object detection
coils 70 may include coils of different winding types. For example,
some of coils 70 may have spiral winding patterns and some of coils
70 may have figure eight winding patterns. Each type of coil may
exhibit different peaks and valleys in sensitivity to foreign
objects, so by overlapping coils with different types of winding
patterns, blind spots can be avoided.
[0038] FIG. 9 is an illustrative foreign object detection coil with
a spiral winding. Conductive path (line) 92 of the winding of
illustrative coil 70 of FIG. 9 has a spiral shape that fits within
a desired coil outline. Coil 70 of FIG. 9 has the shape of a ring
quarter segment. Distance (radius) R is associated with the
distance from the center of coil 36. Wedge shaped coil shapes and
other coil outlines may be used, if desired. Terminals 94 are
coupled electrically to control circuitry 16 (e.g., measurement
circuitry 41). During operation, changes in voltage (.DELTA.V)
across terminals 94 are monitored by circuitry 41 to determine if
foreign object 90 is present. There may be any suitable number of
turns in the spiral coil winding of FIG. 9 (e.g., at least one, at
least two, at least three, at least five, at least 10, fewer than
20, etc.).
[0039] FIG. 10 is an illustrative foreign object detection coil
with a figure eight winding. Conductive path (line) 96 of
illustrative coil 70 of FIG. 10 has an outline with the shape of a
ring quarter segment (as an example). The use of a common shape for
coil 70 of FIG. 10 and coil 70 of FIG. 9 (e.g., matching coil
outlines) allows coil 70 of FIG. 10 to overlap and match the
outline of coil 70 of FIG. 9. Other shapes may be used, if desired
(e.g., other shapes such as the wedge shapes of FIG. 6 or other
shapes that match the shape of an overlapped spiral coil).
[0040] Conductive path 96 is coupled to measurement circuitry 41 by
terminals 98. A first portion of coil 70 of FIG. 10 forms a first
subcoil C1 with a first winding sense (e.g., clockwise), whereas a
second portion of coil 70 of FIG. 10 forms a second subcoil C2 with
a second winding sense (e.g., a clockwise winding sense). Because
subcoils C1 and C2 have opposite winding senses, coil 70 of FIG. 10
tends to be sensitive to perturbations in lateral magnetic fields.
This sensitivity is complementary to the sensitivity of coil 70 of
FIG. 9, so by using both coil 70 of FIG. 9 and coil 70 of FIG. 10,
foreign object detection blind spots are avoided. Coils C1 and/or
C2 may each have a single turn (as shown in FIG. 10) and/or coil C1
and/or coil C2 may have two or more turns.
[0041] FIG. 11 is a diagram showing how coil 36 may produce lateral
magnetic fields B1, B1', B2, and B2' during wireless power
transmission. Figure-eight coil 70 has first subcoil C1 and second
subcoil C2 in areas that overlap respective portions of coil 36
(e.g., coil 70 may have a quarter ring segment shape of the type
shown in FIGS. 4 and 5). The behavior of the magnetic fields
associated with coil 36 during operation depends on whether foreign
object 90 is present. In the absence of object 90, coils 36 produce
magnetic fields B1 and B2. Magnetic field B1 has a first portion
that passes upwardly through coil C1 and a second portion that
passes downwardly through coil C2. This induces two voltage
contributions that add constructively to produce a resulting
.DELTA.V value at the terminals of coil 70. Magnetic field B2
passes through coil C1 but not through coil C2, so magnetic field
B2 contributes less to the induced voltage .DELTA.V in this
example.
[0042] In the presence of a magnetic foreign object such as a paper
clip formed from magnetic steel or another object formed from
magnetic material (e.g., foreign object 90 of FIG. 11), magnetic
fields are perturbed. In the example of FIG. 11, magnetic field B1
may follow the path of magnetic field B1' of FIG. 11 in the
presence of foreign object 90, which induces a voltage similar to
that induced in the absence of foreign object 90. On the other
hand, magnetic field B2 now follows the path of magnetic field B2'
of FIG. 11 because the magnetic material of foreign object 90 of
FIG. 11 forms a bridge. As a result, magnetic field B2' passes
upwardly through coil C1 and downwardly through coil C2 and
therefore induces more voltage .DELTA.V than magnetic field B2.
Using measurement circuitry 41, circuitry 16 measures the
difference in the value of .DELTA.V resulting from the presence of
object 90, thereby detecting when object 90 is present.
[0043] FIG. 12 is a graph illustrating the response (.DELTA.V1) of
a spiral foreign object detection coil (e.g., coil 70 of FIG. 9)
and the response (.DELTA.V2) of an overlapping figure eight coil
having the same outline when a foreign object such as a magnetic
foreign object is located at distance R from the center of coil 36.
As shown by the graph, the spiral coil may exhibit a minimum
sensitivity to the presence of foreign objects at distance XM. At
this location, the figure eight coil has a maximum in sensitivity,
so the responses of the coils with different winding patterns are
complementary and detection blind spots are avoided. As this
example demonstrates, the use of overlapping detection coils 70
helps device 12 detect magnetic foreign objects.
[0044] In the presence of a non-magnetic foreign object, the
foreign object may perturb magnetic fields differently. In
particular, instead of forming a bridge for magnetic fields as with
a magnetic foreign object, a non-magnetic foreign object may tend
to block magnetic flux. As a result, induced voltages in coils 70
for coils such as spiral and figure-eight shape coils will tend to
be reduced relative to other coils in the group with no foreign
object present. When flux is blocked in one part of the transmitter
it is increased (net flux is still the same) through other sections
(detection coils) whose voltages in this case are increased. But in
the presence of a magnetic foreign object, flux is perturbed only
around close proximity to the foreign object since it is bridged
rather than blocked.
[0045] In the example of FIGS. 9, 10, 11, and 12, foreign object
detection coils 70 include a first set of coils of a first type
(e.g., a set of four or more spiral coils) and a second set of
coils of a second type that is different than the first type (e.g.,
a set of four or more figure eight coils). These coils may have
quarter-ring-segment shapes or other suitable shapes. Other types
of coil 70 and/or other coil shapes may be used, if desired. The
outlines of coils 70 may overlap completely or partly with each
other and may overlap completely or partly with the windings of
coil 36. The illustrative quarter ring segment coils 70 of FIGS. 4
and 5 completely overlap the windings of coil 36 (e.g., none of the
windings of coils 70 fall outside of the footprint of coil 36),
whereas the illustrative wedge shaped coils 70 of FIGS. 6 and 7
partially overlap the windings of coil 36 and partially overlap the
empty center of ring-shaped coil 36. Coils 70 may include only one
layer of coils (e.g., the coil layer of FIG. 4), may include only
two layers of coils (e.g., a first layer with the pattern of FIG. 4
and spiral windings and a second layer with the pattern of FIG. 4
and matching figure-eight windings), may include three or more
layers of coils, may include coil layers with different coil shapes
and/or orientations (see, e.g., the layers of FIGS. 4, 5, 6, and
7), and/or may include other arrangements of coils.
[0046] The foregoing is merely illustrative and various
modifications can be made to the described embodiments. The
foregoing embodiments may be implemented individually or in any
combination.
* * * * *